1. Field of the Invention
The present invention relates to a by-pass valve in particular for pressure-washing machines.
2. Description of the Prior Art
Pressure-washing machines are normally used for washing using high-pressure water, where the delivery pressure reaches a value of the order of 100 bar or more, and may be used both at ambient temperature and in hot conditions.
A pressure-washing machine is connected to a washing gun generally supplied by a volumetric piston pump designed so as to delivery a constant flow of fluid. This gives rise to a few problems; firstly the operating pressure must be regulated and, since it is measured at the delivery outlet of the machine, it depends on the head losses in the fluid-dynamic circuit present between the pump delivery outlet and the environment; secondly, when the delivery gun is closed, it is necessary to discharge the flow, keeping the delivery pressure of the pump as small as possible so as to reduce the energy consumption and the wear thereof.
The problems listed above may normally be solved by introducing, downstream of the pump, a valve which regulates the washing pressure, discharging a part of the flow, thereby causing by-passing of the entire flow when the gun is closed or in the case where a pressure higher than a threshold pressure occurs inside the system. The by-passed water is conveyed back to the pump supply system.
As mentioned above, the said valve performs at the same time and in the same manner the discharging and safety functions: as soon as the pressure downstream of the valve exceeds a threshold value, the flow is by-passed and the zones respectively downstream and upstream of the valve remain isolated from each other.
The main problem which the abovementioned machines have is the considerable degree of rigidity to which the rubber pipe is subject as a result of the high pressure present inside it when the gun is closed. This limits considerably the ease of handling of the pipe and consequently of the washing gun.
In conventional machines, even after the pump has stopped, a high pressure exists inside the circuit which can be discharged by opening the gun. If the latter operation is not performed and in this situation any joint in the circuit is accidentally removed, there is a violent release of pressure with spray and a dangerous whiplash effect of any disconnected rubber pipes.
If the circuit is left under pressure after use, this causes in the long run damage to the rubber pipe and the gun, in particular in the event of exposure to the sun.
On account of the high pressure present, operation of the gun results in a strong reaction force due to the water flow. Normally there is a sudden delivery of the flow upon opening since the pressure is even higher than the operating pressure; this results in a violent reaction of the gun which may result in a dangerous loss of control by the operator, in particular at higher pressures.
Moreover, since the flow is discharged as soon as the pressure downstream of the valve exceeds a threshold value, the by-pass duct is continuously open and is therefore particularly subject to wear as a result of abrasion by the outflowing fluid.
The object of the present invention is to eliminate the abovementioned drawbacks by providing a by-pass valve in particular for pressure-washing machines, which allows the flow of the pump to be discharged via the by-pass when the gun is closed, allowing at the same time low pressure values in the whole delivery circuit.
A further advantage of the present invention consists in the fact that, by lowering the pressure inside the pipe when the gun is closed, the ease of handling is increased considerably also with respect to the condition where the gun is open.
Moreover, as a result of the present invention, it is possible to avoid problems or damage which may affect the rubber pipe and, in the event of accidental disassembly, also any injury to the user.
With application of the invention, operation of the gun requires a limited amount of force on the part of the operator, the pressure which is to be overcome in this case being limited. This fact, in addition to producing improvements during use, safeguards the activating mechanisms of the gun. In fact, during the transient stage where the gun obturator is opened, there is a limited pressure, a limited flowrate and therefore limited abrasive wear of the mechanisms, which is in particular undesirable during this stage.
In addition to that indicated above, the invention results in a gentle delivery of the flow at the start of each delivery cycle, due to its operating transient, which avoids a violent reaction of the gun and possible loss of control by the operator.
The invention, combined with the valve normally present in the system, prevents the latter from continuously opening the by-pass duct. This limits the wear, due to abrasion, of the outflowing fluid and increases the duration and the efficiency of the valve known as a safety valve.
This therefore results in a pressure-washing machine which is simpler, more reliable and safer to use.
Said objects are fully achieved by the by-pass valve in particular for pressure-washing machines, according to the present invention, as described by the contents of the claims indicated below and in particular comprising means for shutting off the discharge section or the outlet section, which are located inside the chamber and actuated in a reciprocating manner by a difference in pressure and by resilient means and provided with means for communication between the inlet section and the outlet section operating during discharging of the flow through the discharge section.